1. Field of the Invention
The present invention relates to an arc tube for a discharge lamp device in which a region including at least a molybdenum foil of an electrode assembly having an electrode, the molybdenum foil and a molybdenum lead wire connected integrally in series is sealed and fixed to a primary pinch seal portion and a secondary pinch seal portion on both ends respectively and the electrodes are opposed to each other in a central sealed chamber portion filled with a luminescent substance, and to a method of manufacturing the arc tube for a discharge lamp device.
2. Description of the Related Art
FIG. 7 shows a conventional discharge lamp device having such a structure that a front end portion of an arc tube is supported by one lead support 3 protruded forward from an insulating base 2, a rear end of the arc tube 5 is supported in a concave portion 2a of the base 2, and a portion of the arc tube 5 provided close to the rear end thereof is held by a metal support member S fixed to a front surface of the insulating base 2. A front end side lead wire 8b led from the arc tube 5 is fixed to the lead support 3 through welding, while a rear end side lead wire 8a penetrates through a bottom wall 2b formed in the concave portion 2a of the base 2 and is fixed through welding to a terminal 9 provided on the bottom wall 2b. The symbol G denotes a cylindrical ultraviolet radiation shielding glove which serves to cut a ultraviolet component having such a wavelength area as to be harmful to a human body in light emitted from the arc tube 5 and is integrally welded to the arc tube 5.
The arc tube 5 has such a structure that electrodes 6 are provided opposite to each other between a longitudinal pair of pinch seal portions 5b and a sealed chamber portion 5a filled with a luminescent substance is formed. A molybdenum foil 7 for connecting the tungsten electrodes 6 protruded into the sealed chamber portion 5a and molybdenum lead wires 8a and 8b led from the pinch seal portions 5b is sealed and fixed into the pinch seal portions 5b. Thus, airtightness can be maintained in the pinch seal portions 5b and 5b. 
More specifically, it is desirable that the electrode 6 should be formed of tungsten having a high durability. However, the tungsten has a very different coefficient of linear expansion from that of glass, is less stuck to the glass and has a poor airtightness. Accordingly, when the molybdenum foil 7 having a coefficient of thermal expansion approximating to that of the glass and stuck comparatively well to the glass is connected to the tungsten electrode 6 and is then sealed at the pinch seal portion 5b, the airtightness of the pinch seal portion 5b can be maintained.
As a method of manufacturing the arc tube 5, first of all, an electrode assembly A having the electrode 6, the molybdenum foil 7 and the lead wire 8 connected integrally is inserted from one of open end sides of a cylindrical glass pipe W having a spherical swollen portion w2 formed in the middle of a linear extended portion w1 and a position q1 in the vicinity of the spherical swollen portion w2 is subjected to primary pinch seal as shown in FIG. 8A. As shown in FIG. 8B, then, a luminescent substance P is put into the spherical swollen portion w2 from the other open end side. As shown in FIG. 8C, subsequently, another electrode assembly A is inserted and a position q2 in the vicinity of the spherical swollen portion w2 is heated and is subjected to secondary pinch seal while the spherical swollen portion w2 is cooled with liquid nitrogen such that the luminescent substance is not vaporized. Thus, the spherical swollen portion w2 is sealed. Consequently, the arc tube 5 having a chipless sealed chamber portion 5a is completed. At the primary pinch-sealing step shown in FIG. 8A, an antioxidant gas (generally, an inert gas or a reducing gas) is supplied into the glass pipe W to carry out the pinch seal such that the electrode assembly A is not oxidized. At the secondary pinch-sealing step shown in FIG. 8(c), the open end is sealed as indicated by the reference numeral q3. Consequently, a discharge starting gas introduced into the glass pipe W is filled in the glass pipe W and the spherical swollen portion w2 is cooled with the liquid nitrogen such that the discharge starting gas and the luminescent substance are not vaporized. Thus, the glass pipe W is almost evacuated to carry out the pinch seal.
In the conventional method of manufacturing an arc tube, however, the vicinity of a boundary between the molybdenum lead wire 8a led from the primary pinch seal portion (the pinch seal portion on the rear end side) and the pinch seal portion particularly becomes fragile so that a mechanical strength thereof is reduced. Consequently, a disconnection is easily caused.
The present inventor has investigated the cause of the drawback. Although the antioxidant gas is introduced into the glass pipe W in order to prevent the electrode assemblies A from being oxidized during the primary pinch seal, it is not led to the open end side of the linear extended portion w1 in a lower portion immediately after the next pinch seal. Consequently, it has been confirmed that the molybdenum lead wire 8 set in a high temperature state is oxidized in contact with oxygen in the air or a part of a molybdenum structure is evaporated or recrystallized due to a high temperature and is therefore made fragile.
JP-A-10-27574 has disclosed a structure in which pinch seal is carried out by supplying an antioxidant gas from a gas supply nozzle having a smaller diameter toward an open end on an electrode assembly A insertion side of a glass pipe at a primary pinch-sealing step. With such a structure, however, the antioxidant gas supplied from the gas supply nozzle partially hits against the lead wire 8 but the whole lead wire 8 cannot be covered. Therefore, it is impossible to effectively prevent the lead wire from becoming fragile.
In consideration of the drawbacks of the related art, it is an object of the present invention to provide an arc tube for a discharge lamp device in which a mechanical strength of a molybdenum lead wire in a primary pinch seal portion is not reduced, and a method of manufacturing the arc tube for a discharge lamp device.
In order to achieve the above-mentioned object, a first aspect of the present invention is directed to an arc tube for a discharge lamp device in which a region including at least a molybdenum foil of a pair of electrode assemblies having an electrode, the molybdenum foil and a molybdenum lead wire connected integrally in series is sealed and fixed to a primary pinch seal portion and a secondary pinch seal portion on both ends, and the electrodes are provided opposite to each other in a central sealed chamber portion filled with a luminescent substance and the lead wire is led from the pinch seal portions on the both ends, wherein, in the primary pinch seal portion, an electrode assembly insertion region of a glass pipe for the arc tube is pinch-sealed with the whole electrode assembly inserted into the glass pipe held in an antioxidant gas atmosphere so that the lead wire has a tensile strength of 10000 kgf/cm2 or more.
If the tensile strength of the lead wire is less than 10000 kgf/cm2, an environment-proof property against vibrations, impacts and an external change in a temperature and a lifetime characteristic against a change in a temperature caused by turning on and off are affected. Therefore, it is desirable that a tensile strength of 10000 kgf/cm2 or more should be maintained.
The lead wire on the primary pinch seal portion side is held in the antioxidant gas atmosphere having no oxygen during the primary pinch seal. Therefore, the oxidation can be prevented and cooling is also carried out with the antioxidant gas at the primary pinch-sealing step. Consequently, it is possible to prevent a molybdenum structure from being evaporated and recrystallized. More specifically, the lead wire can be prevented from being fragile so that the original mechanical strength of the molybdenum lead wire, that is, a tensile strength of 10000 kgf/cm2 or more can be maintained, thereby obtaining a high durability.
A second aspect of the present invention is directed to the arc tube for a discharge lamp device according to the first aspect of the present invention, wherein the primary pinch seal portion is formed by inserting and providing the electrode assembly such that a tip of the electrode is protruded from an open end of the glass pipe into a chamber portion, provisionally pinch-sealing a side of the molybdenum foil to which the lead wire is to be connected, then holding the inside of the glass pipe in a vacuum state, and regularly pinch-sealing a portion of a region to be primarily pinch-sealed which has not been pinch-sealed.
During the regular pinch seal in the primary pinch seal, a negative pressure in the glass pipe, as well as the press force of a pincher, acts on the heated and softened glass layer, and the glass layer is welded to the surface of the molybdenum foil by pressure and is fixed in contact without a clearance.
Moreover, the lead wire is held in the antioxidant gas atmosphere during the regular pinch seal after the provisional pinch seal as well as the provisional pinch seal at the primary pinch-sealing step. Consequently, the lead wire is not oxidized at the primary pinch-sealing step, and furthermore, is cooled with the antioxidant gas. Therefore, the molybdenum structure can be prevented from being evaporated and recrystallized so that the original mechanical strength of the lead wire can be maintained, thereby obtaining a high durability.
A third aspect of the present invention is directed to the arc tube for a discharge lamp device according to the first or second aspect of the present invention, wherein the secondary pinch seal portion is formed by inserting and providing the electrode assembly such that the tip of the electrode is protruded from the open end of the glass pipe into the chamber portion, removing air in the glass pipe and cooling and liquefying a discharge starting gas filled in the pipe, thereby holding the glass pipe in a vacuum state, and pinch-sealing a region including the molybdenum foil in the glass pipe.
The lead wire on the secondary pinch seal portion side is pinch-sealed in an almost vacuum state in the discharge starting gas atmosphere having no oxygen. At the secondary pinch-sealing step, therefore, the oxidation can be prevented. Moreover, the glass pipe is set in the almost vacuum state. Consequently, the heat of the glass pipe which is heated to have a high temperature is transferred to the electrode assembly (lead wire) with difficulty. In addition, the chamber portion is cooled in order to cool and liquefy the discharge starting gas. Correspondingly, a period for which the lead wire is maintained to have the high temperature can be shortened at the secondary pinch-sealing step and the molybdenum structure can be prevented from being evaporated and recrystallized. Consequently, the original mechanical strength of the lead wire can be maintained and a high durability can be obtained.
Moreover, the molybdenum foil in the secondary pinch seal portion is pinch-sealed in the almost vacuum state. Therefore, a negative pressure in the glass pipe, as well as the press force of the pincher, acts on the heated and softened glass layer during the pinch seal, and the glass layer is welded to the surface of the molybdenum foil by pressure and is fixed in contact without a clearance.
A fourth aspect of the present invention is directed to a method of manufacturing an arc tube for a discharge lamp device comprising a primary pinch-sealing step of inserting an electrode assembly having an electrode, a molybdenum foil and a molybdenum lead wire connected integrally in series from one of open ends of a glass pipe for the arc tube having a swollen chamber portion formed on a middle part in a longitudinal direction such that a tip of the electrode is protruded into the chamber portion, introducing an antioxidant gas from the other open end of the glass pipe into the glass pipe, and pinch-sealing a region including the molybdenum foil in the glass pipe, wherein the primary pinch seal is carried out by inserting an open end of the glass pipe on an electrode assembly insertion side into a gas chamber to which the antioxidant gas is to be supplied and holding the open end of the glass pipe in an antioxidant gas atmosphere.
The antioxidant gas is introduced from the open end of the glass pipe on the electrode assembly non-insertion side into the glass pipe in which the electrode assembly is inserted, and the open end of the glass pipe on the electrode assembly insertion side is exposed to the antioxidant gas in the gas chamber. Consequently, even if the pinch seal portion is maintained to have the high temperature after the primary pinch-sealing step as well as during the primary pinch-sealing step, the molybdenum lead wire is held in the antioxidant gas atmosphere to prevent oxidation and comes in contact with the antioxidant gas to radiate heat so that the molybdenum structure can be prevented from being evaporated and recrystallized. Moreover, the lead wire can be prevented from becoming fragile. Thus, the original mechanical strength of the molybdenum lead wire can be maintained.
A fifth aspect of the present invention is directed to the method of manufacturing an arc tube for a discharge lamp device according to the fourth aspect of the present invention, wherein, in the primary pinch-sealing portion, a side of the molybdenum foil to which the lead wire is to be connected is provisionally pinch-sealed, the glass pipe is then held in a vacuum state, and a portion of a region to be primarily pinch-sealed which has not been pinch-sealed is regularly pinch-sealed.
During the regular pinch seal in the primary pinch seal, a negative pressure in the glass pipe, as well as the press force of a pincher, acts on the heated and softened glass layer, and the glass layer is welded to the surface of the molybdenum foil by pressure and is fixed in contact without a clearance.
Moreover, the lead wire is held in the antioxidant gas atmosphere during the regular pinch seal after the provisional pinch seal as well as during the provisional pinch seal at the primary pinch-sealing step. Consequently, the lead wire can be prevented from being oxidized and the molybdenum structure can be prevented from being evaporated and recrystallized at the primary pinch-sealing step. Therefore, the original mechanical strength of the lead wire can be maintained, thereby obtaining a high durability.
A sixth aspect of the present invention is directed to the method of manufacturing an arc tube for a discharge lamp device according to the fourth or fifth aspect of the present invention, wherein the gas chamber is constituted by an inert gas supply port having a greater size than a bore of the open end of the glass pipe, and is pinch-sealed with the open end of the glass pipe for the arc tube inserted in the antioxidant gas supply port by a predetermined depth such that the open end of the glass pipe for the arc tube does not come in contact with air.
At the primary pinch-sealing step, the open end of the glass pipe is reliably covered with the antioxidant gas supplied from the antioxidant gas supply port so that the molybdenum lead wire extended from the open end of the glass pipe cannot come in contact with the air. Consequently, the molybdenum lead wire can be prevented from being oxidized. Moreover, the flow of the antioxidant gas is generated. Thus, the heat radiating function of the lead wire can be enhanced so that the molybdenum structure can be reliably prevented from being evaporated and recrystallized.
A seventh aspect of the present invention is directed to the method of manufacturing an arc tube for a discharge lamp device according to any of the fourth to sixth aspects of the present invention, further comprising, after the primary pinch-sealing step, a filling substance supply step of supplying a filling substance such as a luminescent substance from the other open end of the glass pipe to the chamber portion and a secondary pinch-sealing step of inserting the electrode assembly having the electrode, the molybdenum foil and the molybdenum lead wire connected integrally in series from the other open end of the glass pipe such that the tip of the electrode is protruded into the chamber portion and pinch-sealing a region including the molybdenum foil of the glass pipe, wherein air in the glass pipe is removed and a discharge starting gas is filled in the glass pipe prior to the secondary pinch-sealing step, and the discharge starting gas is cooled and liquefied to hold the glass pipe in a vacuum state, thereby carrying out the second pinch-sealing step.
The lead wire on the secondary pinch seal portion side is pinch-sealed in the almost vacuum state in the discharge starting gas atmosphere having no oxygen. Therefore, the oxidation can be prevented at the secondary pinch-sealing step. During the secondary pinch seal, moreover, the glass pipe is set in the almost vacuum state. Therefore, the heat of the glass pipe which is heated to have a high temperature is transferred to the electrode assembly (lead wire) with difficulty. In addition, the chamber portion is cooled in order to cool and liquefy the discharge starting gas. Correspondingly, a period for which the lead wire is maintained to have a high temperature can be shortened at the secondary pinch-sealing step. Consequently, the molybdenum structure can be prevented from being evaporated and recrystallized. More specifically, the lead wire can be prevented from becoming fragile so that the original mechanical strength of the lead wire can be maintained.
Moreover, the molybdenum foil in the secondary pinch seal portion is pinch-sealed in the almost vacuum state. During the pinch seal, therefore, a negative pressure in the glass pipe, as well as the press force of the pincher, acts on the heated and softened glass layer. Consequently, the glass layer is welded to the surface of the molybdenum foil by pressure and is fixed in contact without a clearance.